import java.util.Scanner;

public class Main {
    public static void main1(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int count = 0; // 需要买的可乐数
        count = n - (n / 3);
        System.out.println(n + "人共需要买:" + count + "瓶");
    }

    public static void main2(String[] args) {
        System.out.println("********************");
        System.out.println("Very good!");
        System.out.println("********************");
    }

    public static void main1(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();  // 绳子的原长度
        int b = sc.nextInt();   // 绳子的最终长度
        int day = 0;  // 需要的天数
        while (a >= b) {
            a /= 2;    // 每次折半的时候++
            day++;
        }
        System.out.println("Needs: " + day + " days");
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int sum = 0;
        int pinggai = 0;
        int kele = 0;
        while (sum < n) {
            sum++;
            pinggai++;
            kele++;
            if (pinggai % 3 == 0) {
                sum++;
                pinggai = 1;
            }
        }
        System.out.println(kele);
    }
}